This invention relates to fertilizers containing microorganisms and process for producing such fertilizers.
It is known that plants cultivated on a large scale maintain a microflora consisting, for example, of bacteria for fixing nitrogen associated with their roots and that these rhizospheric microflora have an effect of promoting plant growth.
By adding an inoculum of a bacteria of the rhizosphere, a modification of the root development is observed (elongation, dry weight, degree of branching, number of absorbent hairs), a modification of the total dry matter and an increase in the grain yield. These effects are probably due to a combination of several phenomena such as nitrogen fixation, production of plant growth hormones, and pectinolytic activities that make better mineral absorption possible. The influence of the addition of bacteria inocula in the rhizosphere of plants is described, for example, in the article by Gaskins, M. H., Albrecht, S. L. and Hubbel, D. H. Agric. Ecos. Environ. 1984 (12), pp 99-116.
The methods used by the researchers: inoculation in liquid or granular form independently of any other agricultural practice is hard to achieve in the field because of the extra work it would impose on farmers. It has been proposed for cultivation of leguminous plants to package some inocula on some peat and to coat the seeds with the product obtained, but this process has the drawback of putting the microorganisms in direct contact with the different pesticides that generally coat grains. Now, these pesticides most often exhibit a high toxicity with respect to most bacteria species.
It would be advantageous to be able to mix fertilizers and the inocula of rhizosphere bacteria because it has been shown that the effect of an inoculation was better in the presence of mineral, and in particular nitrogenous, fertilizers. Actually, plants having good mineral nutrition exhibit a great deal of root exudation, which promotes the development of rhizospheric microflora. However, up to now the difficulty has been encountered that the inocula did not have sufficient viability upon contact with the fertilizer.